a) Field of the Invention
The invention is directed to an indexer for magazine shelves of a magazine and wafer-shaped objects contained therein, in particular semiconductor wafers and templates or masks, the magazine and a first handling plane for removing and charging being adjustable vertically relative to one another for the processing of such wafer-shaped objects, with an optoelectronic sensor arrangement for detecting the objects and magazine shelves relative to a reference plane which is in a fixed relationship to the first handling plane Such technical solutions are applicable in the manufacture of integrated circuits, in particular for handling tasks, and are known, e.g., from DE 43 06 957 C1.
b) Description of the Related Art
In the manufacture of integrated circuits, wafer-shaped objects such as semiconductor wafers and masks must be transported between different processing stages to individual processing machines. In increasing measure, such transporting takes place in standardized transport containers, referred to as standard mechanical interface boxes (SMIF boxes), the magazine within whose shelves the wafer-shaped objects are located being fastened in a suitable manner to the base of these transport containers. For the purpose of charging the processing machines, the magazines are unloaded from the transport containers by suitable devices and the wafer-shaped objects are removed by a removing and charging mechanism. After processing, the wafer-shaped objects are returned to the shelves of the magazine and the magazine is returned to the transport container.
A disadvantage in the possible use of impact pressure sensors or reflex couplers which act on the rear side of the wafer-shaped objects to detect the latter consists in that the magazine must be handled in a determined sequence. In so doing, the objects may not be removed from the magazine in an arbitrary manner. Rather the charging magazine must be emptied from the bottom up and the dispensing magazine must be filled from the top down because of the required sensor arrangement and the removing and charging of semiconductor wafers associated therewith. Consequently, the allocation of the object to a determined level is not adhered to. Such technical solutions cannot be applied for the conventional removal of random samples for inspection purposes or for use in the above-mentioned transport containers.
It is known from U.S. Pat. No. 4,895,486 to determine the presence of wafer-shaped objects in a carrier (magazine) and their position relative to a reference plane in the carrier by means of a monitoring device in that a first signal indicating the presence of such an object is combined with a position signal for the object. The first signal is obtained by an optoelectronic sensor which monitors the space in which the objects can be found. The second signal is formed via a position encoder coupled with a drive for moving the carrier up and down To determine the reference plane and possible resting place of the objects, the space in the carrier is divided vertically into segments In addition to a segment serving as a reference plane and segments without wafer-shaped objects, window segments in which objects may be present are defined. An indexing of the carrier is effected in that, after the reference plane in the carrier is detected by measuring techniques, the locations of the window segments are determined and stored by computer based on construction data of the respective carrier being used.
Although the quantity of objects and the locations in which they are deposited relative to a reference plane with in the carrier can be determined by means of the described solution, the carrier or the removing and charging mechanism must be positioned in the grid dimension of the shelves of the carrier in order to remove the objects from the carrier. If divergent carrier geometries and tolerances are not allowed for in so doing, errors cannot be ruled out. Problems arise in particular when an empty carrier is to be charged optionally.
Further, it is possible to monitor the correct position of the object in the carrier by means of an additional optoelectronic sensor when the carrier is being transported upward in the vertical direction. This is done in order to prevent damage to objects protruding from the carrier when returning the latter to the transport containers. If it is detected that an object is protruding from the carrier due to defective or incorrect operation of the handling system, the transport of the magazine is halted and manual intervention on the part of the operator is required to eliminate the error. While the detection of protruding or projecting objects has practical importance, the required manual intervention causes unnecessary delays in continued processing by interfering with the clean room conditions and, in some cases, the climatic conditions of the processing machines within the machine enclosure. This can result in failure of the machine.
The solution described in DE 43 06 957 C1 meets all of the demands mentioned above in that the position of the wafer-shaped objects as well as the position of the magazine shelves relative to a reference plane are detected by means of a bundle of measurement rays emitted by an optoelectronic sensor formed of a transmitter and receiver The reference plane is in a fixed constructional relationship with a handling plane for removing and charging. The magazine is adjustable vertically in a measurable manner relative to a handling plane for removing and charging by means of a magazine receiving device via a magazine elevator.
A disadvantage consists in that magazines must be restricted to those in which two opposite sides are freely accessible. This indexing arrangement is not applicable in magazines which are only open at the side serving for removing and charging. Another disadvantage consists in that it is not possible to differentiate directly between different magazine sizes or formats.
Therefore, the problem arises of ensuring accurate access in any desired and predeterminable magazine plane, also for magazines which are provided with an opening on only one removing and charging side, by means of an all-purpose indexing, wherein it is possible to differentiate between various standardized magazine and wafer formats. A primary object of the present invention is to overcome this stated problem.
This object is met, according to the invention, by an indexer for magazine shelves of a magazine and wafer-shaped objects contained therein, in particular semiconductor wafers and masks, the magazine and a first handling plane for removing and charging being adjustable vertically relative to one another for the processing of such wafer-shaped objects, with an optoelectronic sensor arrangement for detecting the objects and magazine shelves relative to a reference plane which is in a fixed relationship to the first handling plane, in that at least a part of the optoelectronic sensor arrangement is designed as a distance measuring system.
If the wafer-shaped objects are opaque frontwise from one edge to the other, the entire sensor arrangement can be designed as a distance measuring system which detects radiation scattered at the edges of the objects and magazine shelves.
In this case, the distance measuring system contains a transmitter and a receiver arranged at an open side of the magazine so that a bundle of measurement rays proceeding from the transmitter with its center ray lying in the reference plane detects successively the wafer-shaped objects and shelf-forming projections for the objects by means of the vertical adjustment of the magazine relative to the reference plane, the objects and the projections being distinguishable from one another because of the different distances relative to the transmitter
As a result of the vertical adjustment, an image of the magazine shelves and of the wafer-shaped objects contained therein is generated by an amplitude modulation of the output signal. This is brought about by the change in the distance between the transmitter and the reflecting item in the reference plane vertical to the direction of movement. The received signal, whose value depends on the distance between the transmitter and the point of incidence, is converted into an analog signal by means of an electronic amplifier.
The sensor system, whose bundle of measurement rays lies in a horizontal plane, determines the vertical position and, by determining the coordinates in the horizontal plane, ascertains whether the item in question is a magazine shelf for a wafer-shaped object or the object itself.
In the case of wafer-shaped objects which are transparent frontwise from one edge to the other, the light scattered in the backward direction can only be measured under certain conditions.
Therefore, the optoelectronic sensor arrangement advantageously comprises a distance measuring system, which is arranged at an open side of the magazine in the reference plane and contains a transmitter and a receiver, and an additional receiver which is arranged at the opposite open side of the magazine. A bundle of measurement rays proceeding from the transmitter is directed on the objects and projections so as to be inclined in the reference plane relative to the vertical incident radiation.
Whereas the distance measuring system serves to detect shelf-forming projections, a parallel-plate effect brought about by the presence of an object can be utilized for detecting the object owing to the arrangement of an additional receiver. The additional receiver can be placed either at the location struck by the bundle of measurement rays if no object is located in the magazine shelf or at the location struck by the measurement ray bundle which is offset owing to the presence of an object.
A sensor arrangement formed of a distance measurement system which contains a transmitter and a receiver arranged at an open side of the magazine, an additional transmitter on the same side, and an additional receiver arranged at the opposite open side of the magazine is also suitable for objects which are transparent frontwise from one edge to the other.
In this sensor arrangement, a bundle of measurement rays proceeding from the additional transmitter is directed only on the object so as to be inclined in the reference plane relative to the vertical incident radiation. The distance measuring system serves to detect shelf-forming projections. The additional receiver is used in the manner described above
The receiver and transmitter of the distance measuring system are advantageously combined in a structural unit.
By means of the technical solution according to the invention, the actually occurring ratios in a magazine to be indexed are determined in that the magazine shelves and the wafer-shaped objects contained therein are detected with measuring techniques. Accordingly, the objects may be removed and restored optionally so at to enable any type of re-sorting or rearrangement between magazines with different shelf spacing as well as with respect to a reference plane within the magazine. Empty magazines can also be filled as desired. The technical solution also allows the use of magazines or magazine-like containers which are closed on all sides but that side having the charging and removing opening.
Given a suitable design of the magazine, which is often ensured at the present time owing to the global standard, different magazine formats can be determined by means of the value of the analog signal alone. The position of the wafer-shaped object can also be valuated in every plane parallel to the reference plane using the value of the analog signal determined by the distance and this valuation can be used to distinguish between wafer sizes or to monitor the correctly positioned depositing of the wafer-shaped object following a handling process or prior to the start of the handling process.
If depositing is not effected in the proper location, a returning device is advantageously provided in a second handling plane parallel to the first handling plane for positioning wafer-shaped objects protruding from the magazine. The actuation of the wafer returning device is contingent upon the value of the sensor signal of the distance measuring system in the case of wafer-shaped objects which are opaque frontwise from one edge to the other. In the case of transparency, another sensor system can be used for detecting objects protruding from the magazine. Triggered by the sensor signal, the wafer returning device guides the object back into the magazine shelf without external intervention. Further transport of the magazine in the transport containers is ensured and damage to protruding objects is prevented without manual intervention.
The invention will be explained more fully in the following with reference to the schematic drawing.